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1. Field of the Invention
Aspects of the invention relate to a method for estimating media thermal decay based on error rate failure criteria.
2. Description of Background Information
One of the biggest problems for high density recording media is media thermal decay. Until now, no one has proposed da feasible method to quantitatively predict media thermal decay lifetime based on real drive level failure criteria. Much of the published literature has discussed how to determine whether a medium is stable or unstable using a media stability factor, KuV/kT, where Ku is anisotropic energy of a media alloy, V is a switching volume, k is a Boltzmann constant, and T is a media temperature. However, no method has been reported that quantitatively determines the media thermal decay lifetime. Some of the reasons for this may be that the previously used failure criteria for media thermal decay is not well defined or directly related to drive performance, lifetime determination was based mostly on modeled results, and simple test acceleration and straightforward extrapolation from accelerated to non-accelerated conditions were never demonstrated.
Other approaches that have been proposed have included:
a) using critical current to detect noise peaks where the magnetic moment reaches zero. See xe2x80x9cThermal Effects and Recording Performance at High Recording Densitiesxe2x80x9d, by M. Alex and D. Wachenschwanz, IEEE Trans. Mag., Vol 35, page 2796 (1999); and
b) using the time dependence of Hc based on the Sharrock equation to estimate decay time. See xe2x80x9cTime Dependence of Switching Fields in Magnetic Recording Mediaxe2x80x9d, by M. P. Sharrock, J. Appl. Phys., vol 15, page 6413 (1994).
An embodiment of the invention is a method for determining a thermal decay lifetime of a machine-readable medium at a given temperature. A test pattern is written to a portion of the medium. An initial amiplitude of signals on the portion of the medium is measured, A first stress magnetic field is applied to the portion of the medium. After applying the first stress magnetic field, a first amplitude of signals on the portion of the medium is measured. The test pattern is rewritten to the portion of the medium. A second stress magnetic field is applied to the portion of the medium. After the applying of the second stress magnetic field, a second amplitude of signals on the portion of the medium is measured. A time to failure is determined corresponding to the first and the second stress, magnetic fields, respectively, the time to failure being an amount of time, measured from a corresponding reference time, for a respective amplitude of the signals on the medium to degrade, in relation to the initial amplitude, beyond a predetermined failure criteria. A time to failure without applying a stress magnetic field is determined based on a relationship between the corresponding times to failure determined for each of the applied stress magnetic fields and Ln(the corresponding times to failure).